It appears that Apple's warning about MacBooks and MacBook Pros running slower …

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There are plenty of tips and tricks that users of Apple products should be aware of, like the fact that iPhones and toilets are not (and will not ever be) friends. A caution against using your MacBook or MacBook Pro without the battery installed may need to be added to that list. While testing some RAM on his MacBook Pro, PC Magazine writer Zach Honig discovered that Apple's notebooks take a rather substantial performance hit whenever the machines do not have batteries installed.

Apple does mention the speed reduction on the Apple Support site, but the description of this behavior is pretty understated and doesn't make it clear just how of a hit it may be. The fact that MacBooks and MacBook Pros do this type of throttling isn't news, but what is surprising is the magnitude of the speed and processing power reduction. In Honig's case, a 2.53 GHz MacBook Pro running on A/C power and without the battery installed received a 37 percent lower score on the Cinebench R10 test suite. 37 percent. Repeat that a few times in your head for effect, if you'd like.

There's undoubtedly discussion to be had about whether Cinebench R10 is a good test for measuring processor speed decreases, but again, we think the magnitude of the decrease speaks for itself. Even if the true speed reduction is 15 percentage points lower, you'd still be looking at more than a 20 percent decrease. Honig also notes that having a dead or almost dead battery may cause the same effect, so you might not want to put off buying that new battery after all. Just remember to keep it inside your MacBook or MacBook Pro at all times.